The present invention relates to a flame retardant polybutyleneterephthalate resin and, more particularly, to a non-halogen-based reaction type phosphorus-based fire retardant retardant and flame retardant polybutyleneterephthalate resin thereof applicable to the frame, housing, socket and connector of electric/electronic equipment or office machines.
In general, polybutyleneterephthalate is applied to the frame, housing, socket and connector of electric/electronic equipment, electric home appliances or office machines because of its excellent chemical resistance, appearance, mechanical properties and electric insulation. Polybutyleneterephthalate, which is useful for various types of products, is required to have fire retardancy for the use purpose in a wide range of applications, awhile fire retardancy is necessary to polyethyleneterephthalate only used for special cases such as fire retardant thread. However, polybutyleneterephthalate is susceptible to combustion in the air because of its limited oxygen index(LOI) being 23, and thus relatively poor in fire retardancy.
There are two known methods for providing fire retardancy to the polybutyleneterephthalate combustible in the air: the one is a blend method in which a fire retardant is added during preparation or molding of polybutyleneterephthalate; and the other is a copolymerization method in which a fire retardant is incorporated with a polybutyleneterephthalate unit through copolymerization.
The blend method utilizes a halogen-based fire retardant, a red phosphorus-based fire retardant, an antimony oxide compound, a phosphorus-based flame retardant, and hydrated metal oxide, which are used either alone or in combination of two or more. In the blend method, however, the flame retardant is slowly released from the product to deteriorate the flame retardancy and a large amount of flame retardant is required even in combination with a flame retardancy synergistic agent or a flame retardant assistant agent, resulting in deteriorated properties and raised costs. The halogen-based flame retardant readily produces a large amount of halogen compounds, especially, halogenated dioxin, which is at issue in recent years. The red phosphorus-based fire retardant is also not an environment-friendly compound because it produces toxic phosphine gas.
Conventionally, halogen compounds having an ester-forming group or phosphorus compound are known as a flame retardant that can be used in the copolymerization method. Especially, phosphorus compounds are superior to halogen compounds in that they have excellent light resistance and hardly produce halogenated compounds such as halogenated dioxin during combustion.
The phosphorus compounds are known to be of a polyester copolymerization type. As disclosed in U.S. Pat. No. 4,157,436, the phosphorus compounds can be used in the preparation of copolymer type flame retardant polybutyleneterephthalate without any problem but cause many problems in the preparation of polybutyleneterephthalate. More specifically, the use of the phosphorus compound in the preparation of polybutyleneterephthalate may deteriorate the polymerization reactivity and cause a reaction of the phosphorus compound and the polymerization catalyst to form a gel and hence deteriorate the catalytic activity of the catalyst. The phosphorus compound also reacts with a diol component of the material, 1,4-butanediol to yield tetrahydrofuran and water, which deteriorate the polymerization rate and prevent the progress of the polymerization reaction. Hence there is no report on the preparation of copolymerization type flame retardant polybutyleneterephthalate.
Unlike the case of polyethyleneterephthalate, the choice of a flame retardant and the polymerization conditions are of great significance in the preparation of flame retardant polybutyleneterephthalate that has excellent flame retardancy, properties and environment-friendly property.
Recently, major electric/electronic companies in Japan are restraining the use of halogen-based flame retardant polybutyleneterephthalate and expect an alternative of the red phosphorus-based flame retardant polybutyleneterephthalate which is still used in many companies. The Japanese government is planning to restrict the use of halogen- or red phosphorus-based flame retardant polybutyleneterephthalate. Furthermore, the use of polybrominated biphenyl, decaphenyl, octaphenyl and pentaphenyl is legally restricted in German and Holland. Nevertheless, halogen- or red phosphorus-based flame retardant polybutyleneterephthalate is still in use, since there is no substitute available in the market.
It is an object of the present invention to solve the problems in preparation of polybutyleneterephthalate using the copolymerization method and to provide a polybutyleneterephthalate resin that is incorporated with an economical and environment-friendly non-halogen-based flame retardant containing no halogen and prepared by copolymerization of a phosphorus-based flame retardant and a butyleneterephthalate unit to have good flame retardancy and remarkably improved properties.
It is another object of the present invention to provide a polybutyleneterephthalate resin in which a deterioration of crystallization rate caused by the use of the phosphorus-based flame retardant is avoidable.
It is further another object of the present invention to provide a polybutyleneterephthalate resin in which a deterioration of mechanical properties caused by the use of the additive type phosphorus-based flame retardant is avoidable.
To achieve the objects of the present invention, there is provided a flame retardant polybutyleneterephthalate resin being prepared by: (a) performing a transesterification reaction of a dicarboxylic acid or its ester derivative and a 1,4-butanediol to yield a oligomer; (b) adding the oligomer with 0.5 to 30 parts by weight of a phosphorus-based flame retardant represented by the following formula I with respect to 100 parts by weight of the dicarboxylic acid or its ester derivative; and (c) reacting a polycondensation reaction in the presence of a polycondensation catalyst to prepare a polybutyleneterephthalate: 
wherein R1 and R2 are same or different and are methyl or butyl including a hydroxyl group.
In another aspect of the present invention, the flame retardant polybutyleneterephthalate resin further comprises a deposited particle-forming material or an inorganic particle material incorporated during the polymerization reaction or after the preparation of the resin lest incorporation of the phosphorus-based flame retardant having the formula I should impair the crystallization rate.
In further another aspect of the present invention, the flame retardant polybutyleneterephthalate resin further comprises a reinforcing material, which is added to the polybutyleneterephthalate resin obtained using the phosphorus-based flame retardant having the formula I.
Now, the present invention will be described in further detail as follows.
The flame retardant polybutyleneterephthalate of the present invention is prepared by reacting dicarboxylic acid or its ester derivative with 1,4-butanediol as starting materials to produce an oligomer, adding 0.5 to 30 parts by weight of the phosphorus-based flame retardant represented by the formula I to the oligomer with respect to 100 parts by weight of the dicarboxylic acid or its ester derivative, and adding a polycondensation catalyst.
Conventionally, a blending method of incorporating a large amount of a red phosphorus type compound as a flame retardant has been adapted to make polybutyleneterephthalate show flame retardancy. In this case, the flame retardant is simply dispersed in the polymer to result in a deterioration of flame retardancy and properties. So, the blending method requires a large amount of the flame retardant or additionally a flame retardant assistant agent.
Only if the phosphorus compound exists in the polymer chain, polybutyleneterephthalate can be more excellent in flame retardancy with a smaller amount of the flame retardant than incorporated by blending. Accordingly, the present invention incorporates a reactive phosphorus-based flame retardant during the melt polymerization in the preparation of a flame retardant polybutyleneterephthalate resin so as to copolymerize the flame retardant in the polymer chain.
Under most conditions, the use of the phosphorus-based flame retardant is problematic in that the polymerization reaction is hard to process due to deteriorated catalyst activity, caused by the phosphorus-based flame retardant, and formation of by-products such as tetrahydrofuran. On the contrary, the present invention solves the problem by copolymerization reaction using the phosphorus-based flame retardant represented by the formula I.
Dicarboxylic acid or its ester derivative that is the principal starting material in the preparation of the flame retardant polybutyleneterephthalate resin of the present invention may be a mixture of two compounds comprising an aromatic dicarboxylic acid selected from terephthalic acid, 2,6-naphthalenedicarboxylic acid, isophthalic acid, phthalic acid and 5-sodium sulfone isophthalic acid, or its ester derivative; and an alicyclic dicarboxylic acid selected from 1,4-cyclohexanedicarboxylic acid and 1,3-cyclohexanedicarboxylic acid, or its ester derivative. Preferably, more than 99 mol % of terephthalic acid or its ester derivative is used in preparation of polybutyleneterephthalate.
Starting materials, i.e., the above-mentioned dicarboxylic acid or its ester derivative and a 1,4-butanediol compound undergo esterification or transesterification to yield an oligomer. Following addition of a phosphorus-based flame retardant represented by the formula I, the oligomer is polymerized in the presence of a polycondensation catalyst at high temperature under vacuum to prepare polybutyleneterephthalate.
When the added amount of the phosphorus-based flame retardant represented by the formula I exceeds 30 parts by weight with respect to 100 parts by weight of the dicarboxylic acid or its ester derivative, the polymerization rate is dropped and the polybutyleneterephthalate thus obtained has an extremely low intrinsic viscosity. According to the present invention, a high-viscosity flame retardant polybutyleneterephthalate can be prepared without a deterioration of the polymerization rate by controlling the type of the catalyst and the addition time of the catalyst and the phosphorus-based flame retardant represented by the formula I.
The content of the phosphorus-based flame retardant represented by the formula I is preferably in the range of 0.5 to 30 parts by weight with respect to 100 parts by weight of the dicarboxylic acid or its ester derivative, most preferably in the range of 1 to 15 parts by weight.
After the completion of the transesterification reaction using the dicarboxylic acid or its ester derivative and a 1,4-butanediol compound as starting materials, the phosphorus-based flame retardant represented by the formula I is added to the reaction mixture and, after less than 2 hours of reaction, the reaction mixture undergoes the polymerization reaction in the presence of a polycondensation catalyst to prepare flame retardant polybutyleneterephthalate.
The transesterification catalyst as used herein may include at least one selected from metal acetates, such as manganese acetate, zinc acetate, cobalt acetate, magnesium acetate, sodium acetate and lithium acetate; metal hydroxides, such as manganese hydroxide, zinc hydroxide, cobalt hydroxide, calcium hydroxide, magnesium hydroxide and sodium hydroxide; and tetraalkyltitanate having a C2-C6 alkyl substituent, which are used either alone or in combination of two or more.
The polycondensation catalyst as used herein may include at least one compound selected from metal oxides, such as antimony oxide, tin oxide or germanium dioxide; tetraalkyltitanate having a C2-C6 alkyl substituent; and metal acetates, such as manganese acetate, zinc acetate, cobalt acetate, magnesium acetate, sodium acetate or lithium acetate, which are used either alone or in combination of two or more.
Due to selection of the phosphorus-based flame retardant represented by the formula I and adequate catalysts and optimized reaction conditions, the flame retardant polybutyleneterephthalate thus obtained contains 0.3 to 5 wt. % of phosphorus atom in the polymer so as to have flame retardancy without a deterioration of crystallinity and processability.
When the polybutyleneterephthalate incorporated with the polymerization type flame retardant of the formula I has the same intrinsic viscosity as homo-polybutyleneterephthalate, it may have a deterioration of the mechanical properties such as Izod impact strength, tensile strength or bending strength due to the bulky copolymer component.
To solve this problem, the present invention may incorporate a reinforcing material such as glass-reinforced fiber or carbon fiber into the polybutyleneterephthalate resin.
In particular, the incorporation of a reinforcing material enhances the mechanical properties most effectively when the polybutyleneterephthalate resin has an notched Izod impact strength of more than 3 kgxc2x7cm/cm, a tensile strength of more than 400 kg/cm2 and a flexual strength of more than 800 kg/cm2.
Preferably, the added amount of the reinforcing material incorporated into the polybutyleneterephthalate resin is in the range of 10 to 50 wt. % with respect to 50 to 90 wt. % of the polybutyleneterephthalate resin.
If the content of the reinforcing material is less than 10 wt. % in the entire polybutyleneterephthalate composition, the incorporation of the reinforcing material hardly enhances the mechanical properties. Otherwise, if the content of the reinforcing material exceeds 50 wt. %, there is a problem in regard to processability during injection molding.
The flame retardant resin obtained by incorporation of the reinforcing material has a notched Izod impact strength of more than 4 kgxc2x7cm/cm, a tensile strength of more than 500 kg/cm2 and a flexual strength of more than 1,000 kg/cm2, in which case it may be adapted to various applications such as the frame, housing, socket or connector of electric/electronic equipment or office machines.
The polybutyleneterephthalate resin composition incorporated with the reinforcing material may exhibit fire retardancy when the LOI is greater than 26.
According to the present invention, a deposited particle forming material or an inorganic particle material is added during the polycondensation reaction in order to prevent a possible deterioration of the crystallization rate of the polybutyleneterephthalate obtained by using the phosphorus-based flame retardant represented by the formula I.
If the content of the phosphorus-based flame retardant represented by the formula I exceeds 5 parts by weight with respect to 100 parts by weight of the starting material dicarboxylic acid or its ester derivative, the flame retardant polybutyleneterephthalate has a remarkable deterioration of the crystallization rate relative to the homo-polybutyleneterephthalate.
To avoid the deterioration of the crystallization rate, a deposited particle-forming material is used to form internal particles during the polymerization reaction, or an inorganic particle material is used during the polymerization reaction or after the preparation of the resin.
Fine inactive particles formed by the deposited particle-forming material or the inorganic particle material acts as a nucleating agent in the resin to enhance the crystallization rate.
Formation of internal particles by the deposited particle-forming material is practicable by incorporation of a metal compound, for example, metal acetate or metal oxide with a phosphorus compound added during the polycondensation reaction. The metal acetate can be used as the above-mentioned transesterification and polycondensation catalyst, and specifically includes manganese acetate, zinc acetate, cobalt acetate. Magnesium acetate, sodium acetate, or lithium acetate, The metal oxide as used herein may include antimony oxide, tin oxide, germanium dioxide, or tetrabutyl titanate. The phosphorus compound as used herein may include trimethyl phosphate.
Preferably, the content of the deposited particle-forming material is in the range of 0.001 to 5 wt. % in the resin composition. If the content of the deposited particle-forming material is less than 0.001 wt. %, the crystallization rate is hardly enhanced otherwise, if it exceeds 5 wt. %, the reverse reaction occurs during the polycondensation reaction of the a resin to deteriorate the properties of the resin.
Specific examples of the inorganic particle material used herein may include at least one selected from titanium dioxide, calcium carbonate, talc, clay, mica, aluminum silicate, silica, calcium metasilicate and alumina trihydrate, which are used either alone or in combination of two or more. Preferably, the inorganic particles material have an average particle diameter of 0.1 to 100 xcexcm. The inorganic particles having an average particle diameter of less than 0.1 xcexcm are currently impossible to form, and those having an average particle diameter exceeding 100 xcexcm have to be added in an extremely large amount to deteriorate the properties of the resin.
Preferably, the content of the inorganic particle material is in the range of 0.01 to 10 wt. % in the resin composition. If the content of the inorganic particle material less than 0.01 wt. %, the crystallization rate is hardly enhanced; otherwise, if it exceeds 10 wt. %, the properties of the resin deteriorate.
An analysis of the crystallization rate of the polybutyleneterephthalate resin incorporated with internal or external particles using a DSC7 (equipped with a cooler) thermal analyzer supplied by Perkin-Elmer Co. reveals that the polybutyleneterephthalate resin must have a recrystallization peak area of less than 9.0 J/g in order to have a crystallization rate that does not deteriorate the intrinsic properties of the polybutyleneterephthalate, and a melting peak area of more than 35 J/g to have a sufficiently high degree of crystallization.
The polybutyleneterephthalate resin exhibits good flame retardancy when the LOI used as a criterion in measurement of the flame retardancy exceeds 25.
As such, the incorporation of a phosphorus-based flame retardant during the polymerization reaction and additionally internal or external particles into the polybutyleneterephthalate resin provides flame retardancy without a deterioration of the crystallization rate of the polybutyleneterephthalate.
Of course, the present invention also incorporates a reinforcing material such as glass-reinforced fiber or carbon fiber into the polybutyleneterephthalate resin in order to enhance the mechanical properties of the polybutyleneterephthalate resin obtained by adding internal or external particles, e.g., notched Izod impact strength, tensile strength or bending strength.